CROSS SECTIONS SCALING LAW FOR H2O IONIZATION BY HIGHLY-CHARGED IONS

BACHI, N.; OTRANTO, S

Buenos Aires

Encuentro; Encuentro Nacional de Dinámica Cuántica en la Materia (DCM-2019); 2019

Instituto de Astronomía y Física del Espacio

Radiotherapy by ion beams, in contrast to photon-beam and electron-beam therapy, allows the irradiation of deep seated tumors with minimal irradiation of surrounding organs andhealthy tissue. This is mainly due to the fact that ions deposit most of the dose just before they stop. The potential interest in this type of therapy has increased in recent years at such a pace that by the year 2021 the number of operational facilities worldwide are expected to double those available in 2016 [1].Ion-therapy can be considered a multiscale process, where the collision processes cover thefirst stage. During these collisions, secondary electrons and free radicals are generated which are responsible for most of the biological damage to the tumoral cells. Hence, an accurate description of the main physical mechanisms leading to electron production is desirable, specially during the planning stage of the irradiation procedurewhich strongly relies on a numerical simulation that uses collisional cross sections as input data.In this work we present results of classical Monte Carlo simulations (CTMC) for H+,He2+, C6+, O8+ and Si 13+ collisions with H2O. The impact energies range from 100 to 1000 keV/amu. The molecular target is modeled by an independent atom picture, where the ten electrons are explicitily considered. The interactions among a molecular center and one electron is represented by Coulomb potential with an effective charge Zeff = sqrt(2|Ei|n^2),where |Ei| is the ionization potential of the molecular orbital considered. The electron-electron correlation is not accounted here due to the clasical inestability ofthe multielectronic target.The present results are compared with experimental data collected during the last fourdecades by several laboratories and with theoretical calculations performed by distorted wave methods [2].Fig. 1 shows the obtained scaling for the total net cross sections (sigma_net = sigma_1-ion + 2 sigma_2-ion + 3 sigma_3-ion + ...) as a function of the impact energy.Additionally we present the scaling reported for total loss cross sections(sigma_loss = sigma_1-ion +sigma_2-ion + sigma_3-ion + ...) for H(1s) target which has a similar ionization potential [3].References[1] M. Dosanjh, Cern Courier 58, 32 (2018).[2] S. Bhattacharjee et al, Phys. Rev. A 96, 052707 (2017).[3] R. E. Olson et al, Phys. Rev. Lett. 41, 163 (1978).[4] S. Otranto, N. Bachi and R. E. Olson, Eur. Phys. J. D 73, 41 (2019).